• Journal of the Korean Institute of Educational Facilities
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• v.18 no.5
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• pp.3-11
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• 2011

In this study, the effect of treating 1-dimensional diffusers on the classroom acoustics was investigated to determine if the diffuser are beneficial for performing the preferred acoustical conditions for speech. A 1/10 scale model of a classroom was used to measure the acoustical parameters, T30, $C_{50}$, STI and SNR in that room. The room acoustical conditions were varied by treating diffusers either on the front or side walls of the classroom. When the diffusers were treated on the side walls around the student's areas, a shorter reverberation time at low frequencies was obtained and resulted in performing uniform reverberation times across the frequency bands. The $C_{50}$ values at mid- and high-frequencies were increased by treating the diffusers either on front or side wall surfaces. The highest STI and SNR values were obtained when the diffuser was treated on the front wall around the teacher's areas. It is found that diffusers are beneficial to increase the intelligibility of speech for the rear seats of the rooms.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.2
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• pp.228-236
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• 2021

In order to understand the underwater noise source factor of the linear pump type forced ejection system, a reduced-model compressed water experiment device was developed. The reduced-model compressed water experiment device consists of a reverberation tank, a linear pump type forced ejection device, and an underwater vehicle. The underwater noise source was selected from the hydraulic ram moving speed, the hydraulic ram/piston pipe spacing, the ejection pipe inlet/water ram area ratio, and the number of water ram inlets. The underwater vehicle was ejected into the reverberation tank by the device. The source level was derived from the measured sound pressure. The source level tends to increase as the hydraulic ram/piston tube spacing and the hydraulic ram moving speed increase. The source level tended to increase as the area ratio was increased, but the level was weak. The number of water ram inlet did not affect the source level.

• The Journal of the Acoustical Society of Korea
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• v.34 no.2
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• pp.146-156
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• 2015

This study investigated how the location of sound absorptive materials and sound diffusers affects the acoustic performance of small auditoriums. It was conducted for a standard model established with the averaged dimension of 36 auditoriums which had opened since 2000 in Daehak-ro, Seoul. In this study, the installation area of finishing materials was calculated upon a back wall which had the smallest installation effective area of finishing materials. To analyze the changes of acoustic performance according to installation location of finishing materials, experiments were carried out using the 1/10 down scale models for 8 cases which were made by classifying the installation location of ceiling and side wall into the front, middle and rear part.The used acoustic parameters were reverberation time (RT), early decay time (EDT), clarity (C80), definition (D50) and speech transmission index (STI). In result, the index related to the amount of reverberant sound (RT, EDT) showed the great changes when evaluating it through just noticeable difference (JND), but the one related to clarity (C80, D50, STI) hardly indicated the changes. In case to obtain short reverberation time, it was most effective to control reverberation time through the side walls when installing sound absorptive and diffusive materials, and side wall front was the location which could get the shortest reverberation time.

• The Journal of the Acoustical Society of Korea
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• v.43 no.4
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• pp.445-454
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• 2024

To detect underwater targets using sonar, sonar performance analysis that reflects the ocean environment and sonar characteristics must be performed. Sonar performance modeling of passive and monostatic sonar can be performed relatively quickly even considering the ocean environment. However, since bistatic and multistatic sonar performance modeling require higher computational complexity and much more time than passive or monostatic sonar cases, they have been performed by simplifying or not considering the ocean environment. In thisstudy, the effects of reverberation and ocean environment in bistatic sonar performance were analyzed using the bistatic reverberation modeling in the Ulleung Basin of the East Sea. As the sonar operation depth approaches the sound channel axis, the influence of the bathymetry on sound propagation is reduced, and the reverberation limited environment is formed only at short distances. Finally, it was confirmed that similar trends appeared through comparison between the simplified and elaborately calculated sonar performance modeling results.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.1
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• pp.28-32
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• 2009

• The Bulletin of The Korean Astronomical Society
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• v.34 no.2
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• pp.46.1-46.1
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• 2009

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.2
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• pp.199-203
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• 2006

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.366-370
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• 2000

• The Journal of the Acoustical Society of Korea
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• v.26 no.3E
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• pp.97-103
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• 2007

We propose a combined STBC (Space Time Block Coding) and AMC (Adaptive Modulation and Coding) in the underwater multipath communication channel. Performance of UAC (underwater acoustic communication) in shallow water is degraded by complicated multipath and reverberation. For this reason, and considering the variability of the ocean channel, we combined STBC and AMC techniques, which are the spatial diversity in a multi-sensor communication system. BER (Bit error rate) of combined STBC and AMC is improved by 5dB when we compare with the BER of a single sensor based system. The proposed system shows a 3dB improvement when we compare it with the BER of the single sensor based system applying the AMC technique only.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.227-230
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• 1999

잔향에 대한 인간의 주관적인 지각을 잔향기 설계에 객관적인 수치로써 반영하는 방법으로, 5 자유도 잔향 모델이 제안된 바 있다[1]. 5자유도 잔향 모델은 잔향에 대한 다섯 개의 객관적인 평가량들을 이용하여 시간에 따른 음 에너지 감쇠 곡선을 근사화한 것이다. 즉 5 자유도 잔향 모델을 이용하여 청취자가 원하는 특성을 갖는 잔향을 객관적으로 묘사할 수 있고, 이는 잔향을 합성할 때 잔향 필터의 설계 기준이 된다. 그러나 이 모델로부터 만들 수 있는 잔향 필터의 개수는 실로 무한하고, 그 중에는 인간이 듣기에 부자연스러운 합성음을 만들어 내는 경우도 있다. 즉 자연스러운 잔향을 만들기 위해서는 잔향 모델 외에도 부가적인 잔향 설계 기준이 필요하다. 시간, 주파수 영역에서 대표적인 특성을 갖는 몇 종류의 원음에 대한 청음실험을 통해, 필요한 잔향 설계 기준을 제시한다.